Refactor custom node implementation, add visitor API and stable unqoted text.

[vldm]

Closes: #13
Closes: #5

• This pr contain a lot of fixes, few of them refactor CustomNode to use ParseRecoverable and ToTokens instead of custom methods.

• New crate rstml-controll-flow was added in order to show how to use CustomNode in real project.

• Added visitor API and refactored html-to-string-macro to use it.

• Added hack for stable to parse unquoted text correctly, this is hidden behind feature gate "rawtext-stable-hack"
  Because hack is using source_text function, it cannot be used if template macro called from generated input.
  Macro matcher module allows extracting html template from macro arguments.

[codecov-commenter]

Codecov Report

Attention: 271 lines in your changes are missing coverage. Please review.

Comparison is base (8f8f199) 76.93% compared to head (8378681) 71.26%.

Files	Patch %	Lines
src/visitor.rs	68.38%	49 Missing ⚠️
rstml-control-flow/src/escape.rs	75.00%	35 Missing ⚠️
rstml-control-flow/src/lib.rs	17.07%	34 Missing ⚠️
src/rawtext_stable_hack.rs	69.52%	32 Missing ⚠️
rstml-control-flow/src/tags.rs	81.53%	24 Missing ⚠️
src/node/raw_text.rs	44.11%	19 Missing ⚠️
src/parser/recoverable.rs	54.76%	19 Missing ⚠️
src/parser/mod.rs	40.00%	18 Missing ⚠️
src/node/mod.rs	57.57%	14 Missing ⚠️
rstml-control-flow/src/extendable.rs	78.72%	10 Missing ⚠️
... and 4 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #44      +/-   ##
==========================================
- Coverage   76.93%   71.26%   -5.67%     
==========================================
  Files          12       18       +6     
  Lines         750     1507     +757     
==========================================
+ Hits          577     1074     +497     
- Misses        173      433     +260     

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